The present invention relates to a dust collector which is designed to collect a dust in the outside air, a dust in a room or the like in an air-conditioning field and an industrial field, and which is provided with a charging section for electrostatically charging a dust without utilization of a corona discharge, wherein ozone is hardly generated, and to an air-conditioning system including such a dust collector.
There is such a conventionally known dust collector, for example, described in Japanese Patent Laid-open No. H6-31200. The conventionally known dust collector will be described below with reference to FIG. 8. As shown in FIG. 8, a charging section 101 comprises a linear electrode 102 and an earthed electrode plate A103. A dust-collecting section comprising a voltage applied electrode plate 105 and an earthed electrode plate B106 is mounted at a location downstream of the charging section 101 in an air-flowing direction. In usual, a voltage is applied to each of the linear electrode 102 and the voltage-applied electrode plate 105 by a high-voltage regulated power supply 107, so that there is a difference in potential in a range of 5 to 15 kV between the linear electrode 102 and the earthed electrode plate 103 in the charging section 101, and there is a difference in potential in a range of 2 to 6 kV between the voltage-applied electrode plate 105 and an earthed electrode plate B106 in the dust-collecting section 104.
In such arrangement, a high voltage is applied to the linear electrode 102 in the charging section 101, whereby a very intensive electric field is produced in the vicinity of the linear electrode 102. Therefore, a substance contained in air and having an electric charge collides with molecules of air, whereby electrons are separated from the molecules of air, and separated electrons are deposited to the air molecules to become ionized air. This is called the ionization of air herein. Air present as an insulating material between the earthed electrode and the linear electrode produces a dielectric breakdown and as a result, the ionization of the air occurs, while being accompanied by a large uniform discharged current. Such a discharging phenomenon is called a corona discharge. Ionized air produced by the corona discharge is deposited to a dust contained in the air supplied to the dust collector to electrostatically charge the dust. The electrostatically charged dust is introduced along a flow of fed air into the dust-collecting section 104 and deposited to either of the electrode plates under a force of an electric field between the voltage-applied electrode plate 105 and the earthed electrode plate B 106. In this manner, the dust is removed, and the cleaned air is blown out from the rear of the dust-collecting section 104. In the above conventional example, the linear electrode is illustrated as a discharging electrode, but even if another electrode having a shape forming an uneven electric field, e.g., a needle-shape is used, a corona discharge occurs likewise in a state in which a uniform current flows between a tip end of the needle-shaped electrode and the earthed electrode plate A 103, whereby a dust is electrostatically charged and removed in a similar mechanism.
There is also a conventionally known dust collector of a type in which the dust-collecting section 104 is replaced by a filter 108. Such conventionally known dust collector will be described below with reference to FIG. 9. As shown in FIG. 9, a charging section 101 comprising a linear electrode 102 and an earthed electrode plate A 103 and a filter 108 are mounted in the named order in an air-flowing direction. A conductive lattice plate 109 is placed at a location downstream of the filter 108 and connected to earth. Usually, a voltage is applied to the linear electrode 102 by a high-voltage regulated power supply 107, so that there is a difference in potential in a range of 5 to 15 kV between the linear electrode 102 and the earthed electrode plate A 103 in the charging section 101.
In the above arrangement, a corona discharge is produced in the vicinity of the linear electrode 102 in the charging section 101 to electrostatically charge a dust and at the same time, an electric field is generated between the linear electrode 102 and the lattice plate 109 by applying a voltage to the linear electrode 102, whereby a filter medium of the filter 108 is polarized by the electric field. The electrostatically charged dust introduced into the filter receives a force for causing the dust to flow along a polarized electric field within the filter medium toward a surface of a filter medium fiber. As a result, the dust is easy to become collected to the filter medium, and the dust collection performance is enhanced.
Such conventional dust collector is accompanied by a problem that a discharged current in the charging section for electrostatically charging the dust is large. If the discharged current is increased, the amount of power consumed and the amount of ozone (harmful to a human body) generated are increased and for this reason, it is required to electrostatically charge the dust in such a manner that the discharged current does not flow much.
In the charging section of the conventional electric dust collector, a plus voltage is applied to the discharging electrode in order to inhibit the amount of generated ozone. Therefore, the conventional dust collector suffers from a problem that minus ions commonly alleged to provide a good effect of relaxing a human""s frame of mind cannot be released simultaneously with the electrical charging of the dust. Therefore, it is required that minus ions can be released simultaneously with the electrical charging of the dust without flowing of discharged current.
The conventional charging section is generally of an arrangement in which a linear electrode made of tungsten is used as a discharging electrode, and the earthed electrode plate is mounted in an opposed relation to the linear electrode. However, there is a problem that the delivery and reception of an electric charge occurs in all portions of a surface of the linear electrode simultaneously with the ionization of air in the vicinity of the linear electrode and for this reason, useless discharged current flows. Another problem is that the air cannot be ionized efficiently for the reason that it is difficult to intensify the electric field to more than before, because the surface of the linear electrode is smooth. A further problem is that charged particles such as electrons, ions and charged dust particles collide against the discharging electrode, whereby the discharging electrode is liable to be worn, because a high voltage is applied to the discharging electrode and a very intensive electric field is formed in the vicinity of the discharging electrode. Therefore, it is required that the air is ionized efficiently with useless discharged current eliminated, and the collision of the charged particles against the discharging electrode is reduced.
The conventional charging section is designed so that discharged current on the order of 10 to 20 xcexcA per 0.1 m of the linear electrode and on the order of 100 to 200 xcexcA per air flow rate of 1 m3/min is permitted to flow, thereby providing a dust collection efficiency of 80% or more. Even when the needle-shaped electrode is used, discharged current on the order of 100 to 200 xcexcA per air flow rate of 1 m3/min flows, and likewise, a corona discharge is produced to electrostatically charge a dust. If the discharged current of such level flows, the following problem is encountered: the amount of power consumed is large, and ozone is also generated in an amount on the order of 20 ppb to 100 ppb, which is a level not good for the health of a human and which is more than a threshold value of odor, resulting in an uncomfortable ozone odor. Therefore, it is required that the discharged current is reduced remarkably, while ensuring a dust collection performance equivalent to that in the conventional dust collector.
In an air-conditioning system including a dust collector of the above-described type, a flow rate of air is large and a speed of air passing through the inside of the system is also large. Therefore, it is possible to provide a high dust collection performance with a pressure loss kept low by employing, as a measure for adding a dust-collecting function, an electric dust-collecting unit designed so that a dust charged using a corona discharge is collected in a dust-collecting section where the pressure loss is small. However, if the electric dust-collecting unit using the corona discharge is used, the following problem is encountered: The discharged current is larger and hence, the amount of power consumed is also increased. In addition, the amount of ozone generated is also increased to exert an adverse influence to a human""s body and to provide an uncomfortable ozone odor. Even in the air-conditioning system provided with the electrical dust-collecting function, it is necessary to reduce the discharged current.
A charging section in a dust-collecting system of a type having a filter mounted in place of the dust-collecting section suffers from the same problem as that described above. In this case, it is required that a dust is electrostatically charged simultaneously with the polarization of a filter medium, while reducing the discharged current remarkably.
Further, a dust collector having a filter mounted in place of the dust-collecting section suffers from the following problem: As the speed of a dust passing through the filter, i.e., the speed of air flow on a surface of the filter is larger, a dust-collecting effect provided by a force of a electrostatically charged dust flowing along a polarized electric field within a filter medium toward a surface of a filter medium fiber is lost. For this reason, if the speed of air flow on the filter surface is larger, the dust-collecting performance of the filter is not increased, and the pressure loss in the filter is increased. Another problem is that if a lattice plate is not in aligned contact with the surface of the filter, the filter medium cannot be polarized efficiently and uniformly. Even in this case, it is required that the speed of air flowing through the surface of the filter is reduced, and the filter is polarized uniformly.
In addition, there is a problem that if the number of crests of the pleated shape of the filter is increased, it is difficult to work the conductive lattice plate, resulting in an increase in material cost. It is required that even if there is no lattice plate, an earthed surface can be formed at a location downstream of the filter.
It is an object of the present invention to provide a dust collector, wherein the above-described problems associated with the conventional dust collector are solved; a dust can be electrostatically charged in such a manner that the discharged current little flows, thereby ensuring a dust-collecting ability equivalent to that in the conventional dust collector and at the same time, minus ions having an effect of relaxing the frame of mind can be released; the air can be ionized more efficiently; it is possible to prevent the damage of the electrode such as the breaking of the linear electrode due to the deterioration thereof caused by the generation of a corona discharge, the wear of the tip end of the needle-shaped electrode and the like; a enhanced dust-collecting performance can be maintained without being degraded; and wherein when the dust-collecting section is replaced by the filter, a high dust-collecting performance can be maintained, while reducing the amount of power consumed remarkably, and an air-collecting system including a dust collector having the above-described features.
To achieve the above object, according to a first aspect of the present invention, there is provided a dust collector comprising an ion-releasing means for releasing ions without generation of a corona discharge, and a dust-collecting section placed at a location downstream of the ion-releasing means.
With the above arrangement of the dust collector according to the present invention, a dust can be electrostatically charged in such a manner that the discharged current hardly flows.
According to a second aspect, in addition to the feature of the dust collector of the first aspect, the ion-releasing means releases minus ions.
With the above feature of the collector according to the present invention, a dust can be electrostatically charged in such a manner that the discharged current hardly flows, and minus ions having an effect of relaxing the frame of mind can be released.
According to a third aspect, in addition to the feature of the dust collector of the first aspect, the ion-releasing means includes a single or a plurality of discharging electrodes which are linear electrodes, and earthed electrodes mounted on opposite sides of the linear electrode, the electrode connected to earth to provide discharged current of 1 xcexcA or less per 0.1 m of the linear electrode upon application of a high voltage to the linear electrode, the earthed electrode being coated with an insulating material or a semiconductor.
With the above feature, a corona discharge is inhibited, and an amount of discharged current more than required is not permitted to flow, whereby the air can be ionized efficiently, and the collision of charged particles against the discharging electrode can be reduced.
According to a fourth aspect of the present invention, in addition to the feature of the third aspect, the ion-releasing means releases minus ions.
With the above feature, a dust can be electrostatically charged with little flowing of discharged current, and minus ions having an effect of relaxing the frame of human""s mind can be released.
According to a fifth aspect of the present invention, in addition to the feature of the first aspect, the ion-releasing means includes a single or plurality of discharging electrodes which are needle-shaped electrodes having sharp tip ends.
With the above feature, an intensive electric field can be collected at one point per one electrode by forming the discharging electrode into a needle-shape, thereby limiting a electrode portion capable of delivering and receiving a charge. Thus, the corona discharge is inhibited to eliminate useless discharged current. In addition, by forming a very intensive electric field at a sharp tip end portion, the air can be ionized further efficiently, and at the same time, the collision of charged particles against the discharging electrode can be reduced.
According to a sixth aspect of the present invention, in addition to the feature of the fifth aspect, the ion-releasing means releases minus ions.
With the above feature, a dust can be electrostatically charged with little flowing of discharged current, and minus ions having an effect of relaxing the frame of human""s mind can be released.
According to a seventh aspect of the present invention, in addition to the feature of the fifth aspect, an insulating material or semiconductor is mounted around a tip end portion of the needle-shaped electrode to produce no corona discharge.
With the above feature, a corona discharge is inhibited, and useless discharged current is further eliminated, whereby the air can be ionized efficiently, and the collision of charged particles against the discharging electrode can be reduced.
According to an eighth aspect of the present invention, in addition to the feature of the fifth aspect, the discharged current per one needle-shaped electrode is 1 xcexcA or less.
With the above feature, no corona discharge is produced, and an amount of discharged current more than required is not permitted to flow, whereby only ions can be released efficiently, and at the same time, the collision of charged particles against the discharging electrode can be reduced.
According to a ninth aspect the present invention, in addition to the feature of the fifth aspect, one or less needle-shaped electrode is disposed per area of 40 mm square on an air flow surface.
With such feature, the discharged current can be reduced, while ensuring a dust collection performance equivalent to that in the conventional dust collector.
According to a tenth aspect of the present invention, in addition to the feature of the fifth aspect, a conductive lattice plate connected to earth is placed at a location downstream of the needle-shaped electrode, and a filter comprising a filter medium constituting the dust-collecting section is mounted between the needle-shaped electrode and the lattice plate.
With the above feature, by placing a filter having an insulating property and a polarizability in an electric field formed between the needle-shaped electrode and the lattice plate, the filter medium of the filter can be polarized and at the same time, a dust can be electrostatically charged, while reducing the discharged current remarkably.
According to an eleventh aspect of the present invention, in addition to the feature of the tenth aspect; the filter and the conductive lattice plate are formed into a pleated shape and disposed in such a manner that they are superposed one on another.
With the above feature, the flow speed of air on the surface of the filter can be reduced by forming the filter into the pleated shape, and the filter medium of the filter can be polarized efficiently and uniformly by forming the lattice plate into the pleated shape in conformation with the surface of the filter and superposing the lattice plate onto the filter in conformation with the surface of the filter.
According to a twelfth aspect, in addition to the feature of the fifth aspect; a filter comprising a filter medium is mounted at a location downstream of the needle-shaped electrode, the filter having a conductive layer formed thereon by applying a conductive coating onto a downstream surface of the filter, the conductive layer being connected to earth.
With the above feature, an earthed surface is formed on the downstream surface of the filter without provision of a lattice plate.
According to a thirteenth aspect of the present invention, in addition to the feature of the twelfth aspect, the filter is formed into a pleated shape.
With the above feature, the speed of air on the surface of the filter can be reduced by forming the filter into the pleated shape, and the filter medium of the filter can be polarized efficiently and uniformly.
According to fourteenth aspect of the present invention, there is provided an air-conditioning system comprising a dust collector according to any of the previous aspects.
With the above arrangement, the amount of power consumed and the amount of ozone generated can be reduced, whereby the air-conditioning system has a high dust collection performance.
According to a fifteenth aspect of the present invention, there is provided an air-conditioning system comprising a dust collector according to any of the fifth to thirteenth aspects, the dust collector being provided with a needle-shaped electrode mounted directly on a grille to provide a dust-collecting function of electrostatically charging a dust and collecting the dust in a dust-collecting section provided within the dust collector. In the air-conditioning system of the above arrangement, the grille and the needle-shaped electrode are integral with each other, and the dust-collecting section is incorporated in the air-conditioning system in such a manner that it is separated from the needle-shaped electrode.
In the air-conditioning system of the above arrangement, the grille and the needle-shaped electrode are integral with each other, and the dust-collecting section is incorporated in the air-conditioning system in such a manner that it is separated from the needle-shaped electrode.